1. Field
Aspects of the present invention relate to antenna arrays, and particularly, collinear antenna arrays.
2. Description of Related Art
Collinear antenna arrays have many applications and are often used for aerodynamic applications. An exemplary collinear antenna array includes an array of dipole antennas mounted in such a manner that the corresponding antenna filaments of each antenna are parallel and collinear along a common line or axis. A collinear antenna array may be mounted vertically or horizontally in order to increase overall gain and directivity in the desired direction. However, placing a collinear antenna array in close proximity to its support structures typically results in a tradeoff between bandwidth and/or efficiency. Requirements for antenna arrays to be both compact and wideband generally oppose one another so that optimizing one requirement often negatively affects the other requirements. This is a particular problem for UHF and VHF antenna arrays in which wavelengths range from meters to tens of meters. Some applications such as an airborne platform cannot afford even a meter of added space to house a wideband antenna array on the vehicle or in an external pod. Prior antenna designs have been developed and have failed to meet the desired requirements, which are to be low profile, have a wide bandwidth, and have the ability to support frequency scan as required for a phased array sensor system.
Alford (U.S. Pat. No. 4,031,537) discloses an end fed array of collinear dipoles that can be placed less than a quarter wavelength from a host reflector, but have limited bandwidths. In addition, end fed arrays such as those disclosed in Alford are limiting in beam agility over bandwidth when used with phased arrays.
Canonico (U.S. Pat. No. 4,749,997) discloses a modular antenna array that overcomes the end feed limitation, with parallel fed elements that can be mounted in close proximity to the leading edge of a wing with the aid of collinear dipole elements and Yagi directors. Parasitic directors such as Yagi, or similar directors have the ability to guide energy away from a host, allowing a low profile installation, but Yagi type directors are known to have limited bandwidths.
Marino (U.S. Pat. No. 6,043,785) discloses a slot antenna arrangement that improves upon the limited bandwidth of parallel feed co-linear arrays by proposing flared notches with a balun. Likewise, Lee et al. (U.S. Pat. No. 5,841,405, co-invented by the Applicant and assigned to the same assignee of the instant application) teaches a collinear array of flared bunny ears with improved baluns for wide bandwidth; however both of these designs and similar notch elements often proposed for this type of problem suffer with large size due to their long radiators which are not often suitable for an integrated extreme low profile installation on a host platform.
Other parallel fed collinear antenna arrays such as those disclosed by Kaegebein (U.S. Pat. No. 6,057,804) attempt to solve the above problem with designs capable of tunings over a broad band, but with operating bands relatively small compared to the proposed antenna arrays of the present invention. Apostolos et al. (U.S. Pat. No. 6,839,036) is yet still another attempt to tune a broadband notch element for lower profile operation, but even this design is only of minor improvement.
Still other planar arrays such as an antenna arrays using long slot apertures as disclosed by Livingston et al. (U.S. Pat. No. 7,315,288), which is a “current sheet antenna,” have been shown to be both wideband and low profile, but all such examples require a 2-dimensional array of elements with a square footprint of at least ½ wavelength. In many cases these larger footprints would be too large in one dimension to mount on an aircraft wing or inside an aerodynamic pod for the lower UHF and VHF frequencies.
In all prior attempts known to the Applicant to solve the above discussed problems, the lattice spacings are held to be approximately within the range of a quarter to half wavelengths. However, denser packing lattice is still desired.